Previous reports on magneto-optical (the coupling of light and magnetism) effects in nanocrystalline materials has demonstrated the advantages of intentionally doping a system with a magnetic impurity like Mn2+. The doping might allow the host nanocrystal system to maintain its original optical properties with the added benefits of the magnetism derived from the transition metal impurity. A drawback of this approach, however, is the difficulty involved in incorporation of the dopant (transition metal) into the nanocrystal. Therefore, it would be very beneficial to obtain the sought after magneto-optical effects (optical properties remain the same while a magnetic effect is added) that are observed in systems incorporating transition metal impurities, without the inclusion of a transition metal impurity.
The importance of the nanocrystalline form of CdSe as an optical material has been well documented in the relevant literature over the last two decades. These studies have allowed researchers to exploit the size-tunable properties of CdSe quantum dots (QDs) via production of optical materials such as light emitting diodes, photovoltaics, and lasers. In turn, recent efforts have aimed to move beyond optical materials and produce magnetic materials based on CdSe.
One inherent difficulty in producing a magnetic CdSe material exists with the fact that CdSe is a native diamagnetic semiconductor and, therefore, any magnetic effects must be induced by an external source, such as a chemical dopant. To this end, many recent studies have been focused upon producing high quality transition metal doped CdSe QDs in the hope of fabricating new magnetic CdSe materials. A potential drawback, however, in chemical doping of QDs is the possibility that the dopant will disturb the optical properties of the host QDs. For instance, a reduction in the photoluminescence (PL) quantum yield was observed in Co doped CdSe QDs while a complete quenching of the band edge PL was observed in Cu doped CdSe QDs. A second difficulty in producing magnetically ordered nanoparticles is the evolution even in ferromagnets from multi-domain to single domain to superparamagnetic behavior as particle size decreases.
It would be desirable, therefore, to produce magnetic CdSe that retains the native optical properties observed in the undoped material. It would also be desirable to alter a magnetic property of a nanoparticle without requiring doping.